1. Field of the Invention
This invention relates to ultrasonic transducers, and more particularly to an improved two-dimensional ultrasonic transducer and its method of construction.
2. Description of the Prior Art
Ultrasonic transducers of the type currently widely used in the medical field for imaging commonly employ a one-dimensional transducer array, i.e., an array of ultrasonic transducer elements wherein the outgoing sound pulses can be steered and dynamically focused in one direction only. Transducers employing two-dimensional arrays are also known but are not believed to be commercially available despite the increased advantages and the flexibility of use provided by a two-dimensional array.
One problem in developing a commercially feasible two-dimensional ultrasonic transducer array has been the difficulty in providing electrical connections to the individual transducer elements, particularly the connections at the front of the transducer, i.e., the transducer face from which the sound is emitted. Additionally, the relatively high number of individual transducer elements involved in a practical two-dimensional array requires a correspondingly large number of electronic elements for individually driving the respective transducer elements for steering and focusing the beam. Developments in the electronic controls have been made, however, which make it feasible to control a two-dimensional phased array having sufficient transducer elements to provide effective imaging.
The typical ultrasonic transducer used for imaging in the medical field employs a body of piezoelectric material such as PZT sandwiched between one or more backing layers and one or more matching layers. Electric current is provided to the piezoelectric material through conductive ribbons such as thin metal films or polymer films having a coating of conductive metal deposited thereon with the ribbons being attached to the front and back face of the piezoelectric layer before the matching and backing layers are attached. Preferably the piezoelectric body is electroded on its front and back surfaces to assure good electrical connections with the conductive ribbons. The conductive ribbons are routed out the side of the finished transducer for connection to a suitable power supply. One-dimensional arrays of this type may be constructed by initially building a large transducer block having sheets of the conductive film attached to the front and back faces, respectively, of the piezoelectric material, then cutting or sawing the block through the matching layer, piezoelectric layer and attached conductive films, and partially through the backing layer to thereby form an array of spaced parallel transducer elements with the severed conductive ribbon strips providing electrical connection to the back and front faces of the piezoelectric material of each transducer element in the array. In this arrangement, the conductive strips or ribbons extend from the ends of the individual elongated transducer elements in much the same manner as in a single element transducer.
In a two-dimensional transducer array where a plurality of individual transducer elements are arranged in spaced rows extending both longitudinally and transversely to the assembly, it is apparent that the relatively simple current supply system described above cannot be employed to provide power to all the individual transducers in the array. The connections to the back of the transducers in such a two-dimensional array present a particular difficulty because of the necessity to isolate the individual transducers from one another to avoid interference with the sound transmitted by surrounding transducer elements. Accordingly, it is a primary object of the present invention to provide an improved method of producing a two-dimensional ultrasonic transducer array and to an improved ultrasonic transducer array produced by the method.
Another object is to provide an improved method of producing a two-dimensional ultrasonic transducer array including an improved conductor system for providing electrical connections to the piezoelectric element of each transducer while avoiding both electrical and mechanical interference with surrounding transducers.
Another object is to provide an improved two-dimensional ultrasonic transducer array in which the transducer elements are arranged in parallel rows each consisting of a plurality of individual transducer elements, with the rows extending in two directions substantially perpendicular to one another, and to an improved method of producing such a two-dimensional ultrasonic transducer array.